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86 SMT Magazine • August 2016 class racing yachts. Summer 2016 will see these yachts take part in the Americas Cup which is being hosted by the City of Portsmouth, and it is here where the Land Rover BAR team is on a mission to bring the America's Cup back to British waters! The first Workshop session concerned PCBs and circuit technologies. Maartin Cauwe from the Centre for Microsystems Technology, Bel- gium, presented the results of an extensive study into the embedding of passive compo- nents into PCBs for space applications. The reli- ability of such embedded passive components has been evaluated and a functional demon- strator manufactured. It was found the embed- ded technology samples performed almost as well as surface mount technology (SMT) coun- terparts environmentally tested in parallel. It was only the embedded 0201 resistors that had a minor impact on component reliability. At present, standarised testing of such technology is challenging as there are no design rules for space products and, as required by spacecraft contracts, there is no possibility for component replacement or repair with this new technol- ogy. Dr. Cauwe considered further embedding activities should include MOSFETs, power com- ponents and more complex modules. The next presentation concerned the de- velopment of new PCB surface finishes using "deep eutectic solvents" (DESs) based on en- vironmentally benign liquids with remarkably high salt content. This work was described by Karl Ryder from the University of Leicester. DESs have found many applications related to electroplating, electro-polishing, immersion coatings, metal recycling and energy storage. DES technology has enabled the plating of PCB copper tracks with silver, nickel, tin and gold. A so-called "universal surface finish" has been de- veloped by the Leicester team. Its plating chem- istry and main successes were detailed by Dr. Ryder. The main PCB finishes comprise of elec- tro-less nickel, immersion palladium and im- mersion gold (ENIPIG)—these potential space PCB finishes have uniform coverage combined with excellent planarity. The DES processes are free from acids and cyanides, have little effect (dissolution) on the substrate copper and were stated to result in highly solderable surfaces. The reliability of flexible PCBs for aerospace applications was discussed by Hans-Peter Klein of Dyconex AG, Switzerland. Interconnect me- chanical stress testing and exposure to exten- sive temperature cycling was performed on microvias having a diameter of less than 100 microns. It was found that flex materials hav- ing a low Tg could be subject to early in-service damage and their failure mechanisms were de- scribed in detail. Materials with a high Tg were recommended as they are not subject to either the assembly stresses caused by solder-assembly or the conventional spacecraft in-service life stresses. Flexible circuits with a high Tg can undergo rapid acceptance testing and provide meaningful predictions of service life. Other research performed at Swera IVF, Swe- den focused on the cracks that may form in PCB laminate during the thermal cycling of assem- bled electronic components. It was noted by Per-Erik Tegehall that tin-silver-copper (SAC) al- loys are far stiffer than the tin-lead solders they are replacing. One effect, during large delta T thermal cycling of area grid array (AGA) pack- ages mounted to PCBs, is that the SAC solders stress the solder pads far more than the "com- pliant" SnPb solders and this can cause cracks to develop beneath the copper pad terminations. Many reliability tests have been performed at Swera, particularly related to Ball Grid Arrays assembled onto daisy chained monitoring cir- cuits within PCBs. In general, the reliability of the SnPb solders was found to be "lower" than that of the SAC alloys, but it is only when de- 7TH ELECTRONIC MATERIALS AND PROCESSES FOR SPACE WORKSHOP " It was found the embedded technology samples performed almost as well as surface mount technology (SMT) counterparts environmentally tested in parallel. "